n,m,k=map(int,input().split())
q=set([int(x)for x in input().split()])
dp=[0 for i in range(n)]
dp[0]=1 if min(q)==1 else 0
f=lambda x:dp[x]
for i in range(1,n):
    t=dp[:i] if i<k else dp[i-k:i]
    dp[i]=min(t)+(i+1 in q)
print(dp[-1])